Transactions may be distributed over multiple database systems and, in these cases, typically comprise a set of actions. These actions are often organized to conform to the following properties: Atomiticity, Consistency, Isolation, and Durability (ACID). More particularly, data changes within a transaction are typically committed together or are rolled back together (atomiticity). In the case that a transaction is rolled back, the effected resources are returned to the valid state they were in before the transaction (consistency). Any changes made to data by a transaction are invisible to other concurrent transactions until the transaction commits (isolation). Once a transaction is committed, the changes may persist even in the face of subsequent system failures (durability). In order to provide such features and functions, a two-phase commit protocol may be implemented. For example, the X/Open Distributed Transaction Processing Model describes such a two-phase commit protocol in which the transaction manager requests each enlisted resource manager to prepare to commit and, if all resource managers successfully prepare, broadcast a commit decision. The X/Open DTP XA Specification is a software architecture that allows multiple application programs to share resources provided by multiple resource managers and allows their work to be coordinated into global transaction.